Is the Milky Way on a collision course? New clues from Hubble

For decades, astronomers believed the Milky Way was on a definitive collision course with its cosmic neighbor, the Andromeda Galaxy. This collision would eventually obliterate both galaxies and form a massive elliptical galaxy.

However, a new study suggests this catastrophic fate may not be as certain as once thought.

A team of scientists led by Durham University used data from NASA’s Hubble Space Telescope and the European Space Agency’s Gaia Observatory to simulate the dynamic future of the Milky Way and Andromeda galaxies.

The results revise our understanding of galactic evolution, suggesting that the merger may happen much later than previously estimated – and, in fact, may not happen at all.

A shift in galactic destiny

The new study challenges a long-held assumption: that the Milky Way and Andromeda, traveling toward each other at about 100 kilometers per second, were destined to collide in about five billion years.

Instead, after running 100,000 simulations based on updated observations, the team found there is only a 2% chance of a collision within that timeframe.

In just over half of the simulations, the galaxies experienced at least one close encounter. However, astronomers now project a complete merger to occur in eight to ten billion years.

In many other scenarios, the galaxies merely passed each other at great distances and continued on their paths, relatively undisturbed. Moreover, by then, the Sun will have burned out, making any merger irrelevant to life on Earth.

Satellite galaxy alters the collision course

A key factor in the updated forecast is the inclusion of the Large Magellanic Cloud (LMC), the most massive satellite galaxy of the Milky Way.

For the first time, researchers factored in its gravitational influence in a statistically meaningful way. Till Sawala is the study’s lead author and an astrophysicist at the University of Helsinki.

“Although its mass is only around 15% of the Milky Way’s, its gravitational pull directed perpendicular to the orbit with Andromeda perturbs the Milky Way’s motion enough to significantly reduce the chance of a merger with the Andromeda Galaxy,” said Sawala.

In previous models, researchers often relied on single “best guess” values for key variables. This new work used a far broader and more robust method, factoring in the full range of observational uncertainties.

“We’ve simply been able to explore a much larger space of possibilities, taking advantage of new data,” Sawala said. “When we tried to start from the same assumptions as previous researchers, we recovered the same results.”

A revised prediction for our galaxy

The findings imply a significant rethinking of what lies ahead for the Milky Way. “These results are significant for the fate of our galaxy,” said study co-author Alis Deason, a professor at Durham University.

“It used to appear destined to merge with Andromeda forming a colossal ‘Milkomeda.’ Now, there is a chance that we could avoid this fate entirely.” The research builds on our growing ability to model vast galactic systems with increasing precision.

“We see external galaxies often colliding and merging with other galaxies, sometimes producing the equivalent of cosmic fireworks,” said co-author Carlos Frenk, a cosmologist at Durham University.

“Until now, we thought this was the fate that awaited our Milky Way galaxy. We now know there is a very good chance that we may avoid that scary destiny.”

Frenk emphasized the extraordinary nature of these findings. He said it was astonishing that his team was able to simulate the evolution of gigantic collections of stars over billions of years with such precision and figure out their ultimate fate.

“This is a testimony to the power of physics allied to the power of large supercomputers,” noted Frenk.

Galaxy collisions remain a reality

Despite the more optimistic forecast, the authors caution that the future still holds uncertainties. Key variables – such as the transverse motion of Andromeda – are difficult to measure precisely, though upcoming Gaia data releases are expected to refine these measurements.

The researchers plan to continue their investigations with more detailed scenarios as observational data improves. The simulations were the most comprehensive of their kind to date, but even these powerful models have limits.

Still, the implications of the study are clear: while galactic collisions remain a reality in the cosmos, the fate of our own galaxy is no longer set in stone.

As our tools and observations become more sophisticated, the story of the Milky Way is being rewritten – one simulation at a time.

The study is published in the journal Nature Astronomy.

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